AirSpaceMag.com

Above & Beyond: It’s All Sawdust and Mirrors

Above & Beyond: It’s All Sawdust and Mirrors

Still life with telescope, feline, and feet. Even the National Air and Space Museum uses a Dobsonian telescope to show visitors the sun.
(Phil Scott)

By
Phil Scott

airspacemag.com
June 30, 2010

A few years ago, I wrote in this magazine about Jeffrey Jacobs, a sidewalk astronomer who sets up his telescope on New York City streets and invites passersby to have a look at the night sky (“Moonstruck,” Soundings, Oct./Nov. 2005). New Yorkers buy lots of telescopes, which is odd, because in Manhattan you can see only the moon, the larger planets, and the brightest stars. Some say New Yorkers use their telescopes mostly to gaze into neighboring apartments.

I took a few peeks through Jacobs’ telescope myself, and later, when I moved to Florida, I decided I had to have my own, even if it let me see only the same heavenly bodies as Manhattan dwellers.

The price of high-end amateur telescopes quashed that desire, but then I learned about John Dobson, a former member of a Los Angeles Vedantan monastery who built a telescope from scratch: He ground mirrors from a ship’s glass portholes, mounted them in a cardboard tube from a construction site, and built a telescope mount from scrounged lumber, all for about $5. I called the monastery and left a message for him.

Then I consulted Google and found a site titled “How to Build a Dobsonian Telescope.” It had photos of a cannon-like object and complex-looking calculations about setting focal lengths and whatnot, and recommendations to buy what I couldn’t grind myself. It gave glowing reviews for Murnaghan Instruments of West Palm Beach, Florida. That company’s Web site listed a six-inch Dobsonian Telescope component kit—focusers, finder scope, mirrors, eyepieces, and everything else the homebuilder likely won’t discover in a dumpster—for $229.95. I called to order it, and Pat Murnaghan himself answered.

“Among people who don’t have a lot of money to spend on high-end amateur scopes,” Murnaghan said, “about the only way to get a decent, usable telescope that will let you do something beside stare at a couple of dots is either build a Dob or find a used one. With a store-bought telescope with computer-control nonsense, you have something that’s going to work for a while, then it’s going to break.”
I bought the screws and bolts that the plans said I’d need, and called Murnaghan again to ask where I could get the tube to mount the optics. He reminded me that Dobson had used a molding form for a concrete column. “The big concrete construction companies will throw you out the door,” he told me. “You can find Quik-Tube at Lowe’s.”

Next up: Plywood for the mount. I waved down Jaime, my apartment complex’s maintenance man, scooting around in a golf cart. “I need a half-sheet of plywood,” I said. “I’m building a telescope.” He motioned for me to follow him to the maintenance shed, where he pulled out an L-shape sheet. I took some quick measurements. Bingo. Jaime plugged in the power saw, and I spent the rest of the day measuring and cutting. UPS delivered a box of telescope innards that afternoon.

I studied the assembly plans, a mish-mash of verbiage probably written by a scientist. I spray-painted the inside of the tube flat-black. Then I called Murnaghan. “I’m about to cut first cardboard,” I said, playing on “first light,” what astronomers call the first view from a telescope. He gave me a quick pep talk on building a telescope, adding that I really hadn’t needed to paint the inside, despite what the plans said.

“All Dobsonians are ultimately Newtonian reflectors,” he said. “Sir Isaac did all the work. What Dobson did was bring astronomy to the masses.” Galileo’s 1609 telescope magnified light; in 1668, Isaac Newton built a telescope that gathered light instead, using a large concave “primary” mirror mounted in the far end. After the mirror collected the light, it reflected the compressed image to a smaller flat mirror in the front, which reflected the image to an eyepiece.

“If it’s a Newtonian, why is it called a Dobsonian?”

“A Dob is more of a concept than a design,” he said. “He was working with nothing. His resourcefulness and ingenuity were enough that they ended up calling his a Dobsonian telescope.”